1. Technical Field
This invention relates to a rotor position sensing apparatus for motors for sensing the rotational position of a motor such as a synchronous motor. More particularly, the invention relates to a rotor position sensing apparatus for motors wherein a fine position code is capable of being generated by performing an interpolation between position codes from a sensor provided on a rotor. 2. Description of the Related Art
A rotating field-type synchronous motor, which is composed of an armature serving as a stator and a field pole serving as a rotor, is operable to generate a rotating field by application of a three-phase current to the stator windings (armature windings), with the field pole being pulled by the rotating field so as to rotate at the same velocity as the rotating field.
Though a synchronous motor of this kind has been considered to involve complicated velocity control and control circuitry of a complex construction in comparison with a DC motor, a drive method has recently been developed for effecting torque generation control in a manner equivalent to that of a DC motor, thereby facilitating velocity control of the synchronous motor.
According to this drive method, torque generation is controlled in a manner equivalent to that of a DC motor if the armature current and induced voltage are controlled to have the same phase (i.e., if control is effected in such a manner that the main flux and armature current are rendered mutually perpendicular). To realize such control, it is necessary to sense the position of the field pole (i.e., the phase of the main flux, which is displaced from the phase of the induced voltage by 90.degree.), generate a current command having a phase corresponding to the position, and apply the current command to the armature windings of the synchronous motor.
In general, in order to sense the position of the field pole, a widely adopted arrangement has a pulse coder provided on the rotary shaft of the field pole (rotor). The pulse coder produces a position code corresponding to the rotational position of the rotor and thus allows the rotational position of the rotor to be sensed. The pulse coder is composed of a rotary disk having position codes disposed radially of the the position codes. However, the number of position codes capable of being disposed along the circumference of the coder is limited by resolution, with the number being several hundred at most even if a high-resolution Gray code is used as the position code. The position sensing precision is therefore less than satisfactory, making it difficult to carry out fine control.
Accordingly, an object of the present invention is to provide a rotor position sensing apparatus for motors which, irrespective of a limitation imposed on a number of position codes by the resolution of a sensor for sensing the rotational position of a rotor, readily enables generation of fine position signals surpassing the number of position codes of the sensor.